Collaboration Agreements (Narrative) (Details) (USD $)	3 Months Ended		3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2009 Up-Front Cash Payment Arrangement [Member] Astellas [Member]	Mar. 31, 2012 Up-Front Cash Payment Arrangement [Member] Pfizer [Member]	Dec. 31, 2008 Up-Front Cash Payment Arrangement [Member] Pfizer [Member]	Mar. 31, 2012 Development Milestone Payments [Member] Astellas [Member]	Dec. 31, 2009 Development Milestone Payments [Member] Astellas [Member]	Dec. 31, 2009 Commercial Milestone Payments [Member] Astellas [Member]	Dec. 31, 2008 Collaboration Arrangement [Member] Pfizer [Member]	Dec. 31, 2008 Collaboration Arrangement [Member] Development Milestone Payments [Member] Pfizer [Member]	Dec. 31, 2008 Collaboration Arrangement [Member] Commercial Milestone Payments [Member] Pfizer [Member]	Mar. 31, 2012 Acceptance Of MMA [Member] Application Accepted [Member] Milestone Payments [Member] Astellas [Member]	Mar. 31, 2012 Acceptance Of NDA [Member] Application Accepted [Member] Milestone Payments [Member] Astellas [Member]	Mar. 31, 2012 Approval Of NDA [Member] Application Approved [Member] Milestone Payments [Member] Astellas [Member]	Mar. 31, 2012 Approval Of MAA [Member] Application Approved [Member] Milestone Payments [Member] Astellas [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of sales and medical affairs	50.00%
Non-refundable up-front cash payment			$ 110,000,000	$ 225,000,000	$ 225,000,000	$ 123,000,000			$ 225,000,000
Deferred revenue additions related to development milestones						13,000,000
Eligible to receive milestone payments							335,000,000	320,000,000
Eligible future milestone payments under collaboration arrangement for NDA filing													10,000,000
Eligible future milestone payments under collaboration arrangement for MMA filing												5,000,000
Eligible future milestone payments under collaboration arrangement for NDA approval														30,000,000
Eligible future milestone payments under collaboration arrangement for MMA approval															15,000,000
Percentage of up-front cash payments to licensor						10.00%
Share percentage of developing and commercializing dimebon										60.00%	40.00%
Receivable from collaboration partners	$ 14,515,000	$ 12,545,000